Fix test for LSTransportMessageGetMonitorSerial()

:Release Notes:
test_LSTransportMessageGetMonitorSerial was failed because
miscalculation of message offset. With this patch,
test_transport_message is passed.

:Detailed Notes:
MonitorSerial is set by LSTransportSend() at the end of message with
padding to put 8bytes integer (_LSTransportMonitorSerial) with 8bytes
alignment.
MonitorSerial is get by _LSTransportMessageGetMonitorSerial().
Calculation of _LSTransportMessageGetMonitorSerial() is correct. Exact
same offset and padding size with LSTransportSend(). But,
test_LSTransportMessageGetMonitorSerial() did calculate without header
size(_LSTransportHeader) which is 12(on 32bit system). As a result,
there are 4 byte difference in padding size which in turn cause test
failure.

:Testing Performed:
test_transport_message all passed

:QA Notes:

:Issues Addressed:
[ANG-481] luna-service2 test suite
          LSTransportMessageGetMonitorSerial failed

Open-webOS-DCO-1.0-Signed-off-by: SangWook Han <sangwook.han@lge.com>

Change-Id: I8437bd79f9d978cdc1ba89a9210e43f878c26cb1
Reviewed-on: https://g2g.palm.com/4436
Reviewed-by: DCO Verification
Reviewed-by: SangWook Han <sangwook.han@lge.com>
Tested-by: SangWook Han <sangwook.han@lge.com>
Reviewed-by: Anatolii Sakhnik <anatolii.sakhnik@lge.com>
Reviewed-by: Alekseyev Oleksandr <alekseyev.oleksandr@lge.com>
Tested-by: Alekseyev Oleksandr <alekseyev.oleksandr@lge.com>